Please explain logic of this transparency material nodes
This seems to be some form of crude &quot;Wipe&quot; effect.
By using the object's local Z coordinate as input and running through the Less Than math function it basically makes an horizontal line mask.
In the vector node the X and Y axis Scale value to zero is turned down, which makes it basically output the pure Z axis, as opposed to all axis at once which would give a 45º tilted angle. This has basically the same effect as using a Separate XYZ node.
By linking it to transparency it basically makes the object opaque or transparent above/below a certain Z value defined in the Less Than node.